This invention relates generally to computer systems and more particularly to the power subsystems and clock subsystems employed in computer systems.
As it is known in the art, computers have become ubiquitous. In particular, a common type of computer, the so-called "personal computer", which is based upon microprocessor technology uses a standard microprocessor integrated circuit as the central processor of the computer to provide a system which is portable and generally easily affordable by many types of individuals.
Microprocessors generally are synchronous circuits, that is, they require a repetitive signal, commonly referred to as a clock signal for operation. It is also known that as technology advances, one desire is to provide microprocessors that are capable of operating at higher clock frequencies and have increasing circuit complexity. In a computer system which includes, in addition to the microprocessor, memory and I/O devices, such as an I/O interface coupled to a disk, the other devices in the computer system are typically also synchronous and require generation of clock signals for their operation.
One configuration of a personal computer commonly in use is the so-called "notebook" computer which is a portable computer that operates either under battery power or AC power from an AC power line. When operating under battery power, several problems are associated with so-called notebook computers, particularly those notebook computers which use microprocessors which operate at high clock frequencies and have high levels of circuit complexity. Power consumption increases in proportion to the clock frequency and circuit complexity. Therefore, the power consumption of the microprocessor in such notebook type computers limits the duration of operation under a battery power source between charges.
Moreover, due to the increased power dissipation from the microprocessor, the ability to effectively manage the heat generated from the microprocessor is also a concern since this heat must be dissipated to maintain the microprocessor at an acceptable operating temperature.
In operation of the microprocessor, often long periods of time are consumed as idle time in which the microprocessor is performing no useful work. Thus, even though the processor is in an idle state not performing any useful processing tasks, the processor is consuming power and dissipating heat.
Past attempts to address some of the aforementioned heat and power consumption properties of notebook computers, have included clock control circuits which turn the clock signal off to the microprocessor during periods of time when the computer system is on but the microprocessor is not actively engaged in a processing task.
One problem with this approach is that by turning the clock signal off, certain types of microprocessors may lose information since some of the internal circuitry is dynamic, that is, requires constant refresh. In particular, some complimentary metal-oxide semiconductor-based (CMOS) devices, such as the ALPHA AXP microprocessors manufactured by Digital Equipment Corporation require a minimum clock signal.
A second problem with the above approach when applied to high performance microprocessors having dynamic logic is that it does not take into consideration the temperature of the microprocessor nor the level of processing power required by the microprocessor to adequately perform all of its tasks and still conserve battery charge and maintain an acceptable operating temperature for the microprocessor.
In addition to the power and temperature problems with the aforementioned notebook type of computers, desk top as well as other computer configurations likewise have similar power and temperature considerations. For example, with desk top computers much processor time is spent as idle time, and further often a user of the desk top computer will leave the computer "on" for extended time periods (such as overnight or over a week-end) without performing any useful work. This wastes power which is undesirable from an energy conservation point of view.